Teen Brain on Weed

With marijuana use legal in twenty states and counting, it's possible more Americans will become users and some, addicted. If so, what's the health impact, especially for kids?

One study ranked marijuana number eight for its harmfulness to the user and society. Alcohol, heroin and crack cocaine took the top three spots. But some argue when marijuana use is as common as alcohol and tobacco, it would be just as harmful.

We know the occasional user bears little risk, and short term use hurts short term memory making learning difficult. Motor function is also impaired, so driving and doing certain jobs are risky. At very high doses, marijuana can cause psychosis, and long term use can lead to addiction. Of the people who smoke it daily, a quarter to a half become addicted while just 17 percent of adolescents do.

However, teen brains are highly vulnerable since they're not fully developed. Studies show kids who smoke pot regularly have cognitive impairment and lower IQs.

From lab animals we've learned the active ingredient in marijuana, tetrahydrocannabinol, disrupts the ability of neurons to make connections. Teens who are heavy users also have a smaller hippocampus which inhibits memory and learning. Their prefrontal activity affecting cognitive control is also lowered so they don't plan or problem solve as well. One effect is higher school drop-out rates.

Questions remain about marijuana's connection to deadly disease, its second and third hand smoke, and its impact on pregnant women. It is clear that young people should be wary about this seemingly innocuous drug.